This invention relates generally to improvements in the reinforcement of edge sections of fabrics and more particularly concerns improved, reinforced edge sections of porous nonwoven fabrics used as seed bed covers.
Spunbonded fabrics have been found to be very beneficial and useful to farmers, horticulturists and the like. The flat, porous nature of spunbonded fabrics, along with good flexibility characteristics, has made these fabrics very practical as seed or plant bed covers to protect plants and crops during the initial stages after planting, and to foster their growth in the early periods of development. As a protective cover, the spunbonded fabrics provide temperature control for the seed beds to minimize the effects of unseasonal frosts or excessively high temperatures, lessen the effects of erosion and wash-out due to the elements, and keep away foraging birds and animals; as a porous, open blanket, however, spunbonded fabrics allow rain water, spray materials such as pesticides, fungicides, etc., to penetrate through without removal of the cover, among other advantages.
While the advantages of using a spunbonded fabric as a seed bed cover is attractive to farmers, some problems have arisen in using this or similar types of fabric in the field which indicate that there is room for improvement in this type of product. A number of problems stem from the nature of the spunbonded fabric itself. Spunbonded fabrics are basically flat, planar, lightweight, fabricated materials having randomly formed porous nonwoven structures. These fabrics are commonly made by deposition of continuous filaments in freshly spun condition on a moving conveyor, and are deposited so as to lie in a very intermingled, random arrangement among each other. When deposited, the filaments may inherently stick to each other, be heated or chemically treated so that the filaments will bond to each other at the points of intersection, overlap or cross. Well-known techniques for producing spunbonded fabrics are described in U.S. Pat. Nos. 3,595,731 and 3,368,934.
When these fabrics are used in the field to cover a seed or plant bed, generally only one layer of the fabric provides the coverage. The thickness of the fabric commonly is no more than two or three times the denier of the filaments, or in the neighborhood of 0.005 inch. (0.0127 cm.). While this thickness provides for the many desirable qualities of the seed bed cover, it presents a problem in the manner in which the cover is held down over the seed bed.
Typical spunbonded seed bed covers are produced in lengths up to 100 yards (91.4 m.) and in widths of between 3 and 5 yards (2.74-4.57 m.). The farmer rolls the cover out over the seed bed and fastens the cover to the ground along the sides of the cover at spaced intervals for the entire length of the fabric. As a fastening device, the farmer uses hooks, stakes or pins to protrude through the edges of the spunbonded fabric into the ground. Due to the thin, flat nature of the spunbonded material, the fastening devices used by farmers tend to tear the edges of the fabric initially or after the fabric has been laid down and is exposed to windy conditions.
One manner of reinforcing the sides and ends of flat, lightweight, porous, nonwoven fabrics such as spunbonded fabrics has been described in U.S. Pat. No. 3,769,747. In that patent, the edge portions of the spunbonded fabric are folded over a narrow strip of thermoplastic material which is parallel to the edge of the fabric. The strip is sandwiched between two layers of the spunbonded structure. To close the sandwiched layer, heat may be applied to bond the three layers together or an ultrasonic sewing machine may be used to seal the layers. While the construction of the edge portions of this patent has provided one means for a farmer to affix the cover to the ground, some deficiencies have been noted in the edge portions described therein. For example, the reinforcing strip between the layers on the edge segments has made packaging, folding, handling and transporting of the fabric difficult. To provide sufficient strength of reinforcement at the edges, flexibility, and suppleness have been sacrificed. Also, when the edge layers are sewn together around the strip, the stitching near the inside portion of the strip tends to induce stitch-tear stresses which allow the fabric to tear more readily. When high winds occur, the fabric will tear along the inside stitches, leaving the edge portion affixed to the ground, while the main body of the fabric is free to be flapped over by the wind.